The present invention relates to a pattern forming method of forming a micropattern, e.g., a relatively thick interconnection with a film thickness of about 10 xcexcm, which is used in a semiconductor device or micromachine device.
In a semiconductor device, to integrate elements within a small area with a higher degree of integration, elements and interconnections must be formed with smaller sizes, and a multilayered structure of interconnections must be used. In a micromachine device as well, a multilayered structure is used to realize a three-dimensional structure. In these multilayered structures, all the layers are not uniform-thick flat layers, but some layers have complicated three-dimensional shapes with various patterns. For example, in an LSI, a plurality of elements formed on a silicon substrate are connected to each other with a plurality of interconnection layers formed in a multilayered structure on the elements, thereby forming a circuit. In such a multilayered interconnection structure, the three-dimensional shape of the interconnection layer is absorbed by an interlayer dielectric film to obtain a flat state, and another interconnection layer is formed on it.
Among techniques of forming flat an interlayer dielectric film and the like on a three-dimensional shape, according to one technique, an interlayer dielectric film is formed on a three-dimensional shape, and after that the projecting portions of the surface of the interlayer dielectric film in which the three-dimensional shape is reflected is selectively removed, thereby planarizing the interlayer dielectric film. According to another technique called damascene, a trench is formed in a flat interlayer dielectric film, and a material for forming a pattern such as an interconnection fills the trench to form a pattern layer such as an interconnection layer. When the interconnection layer is formed, it is already flat. In damascene, chemical mechanical polishing (CMP) is often used in order to achieve a state wherein an interconnection electrode fills a trench.
Formation of a multilayered interconnection structure according to damascene will be briefly described. As shown in FIG. 3A, an insulating film 302 is formed on a substrate 301, and trenches 303 are formed at predetermined portions of the insulating film 302 so as not to extend through the insulating film 302.
As shown in FIG. 3B, a plating seed layer 304 is formed on the surface of the insulating film 302 including the interiors of the trenches 303. After that, as shown in FIG. 3C, the surface of the insulating film 302 including the interiors of the trenches 303 is plated, thereby forming an interconnection metal film 305 through the seed layer 304.
Finally, as shown in FIG. 3D, the interconnection metal film 305 is polished by CMP until the surface of the insulating film 302 is exposed, while leaving the interconnection metal film 305 only in the trenches 303, thereby forming interconnection layers 306. In CMP, if the metal film is selectively polished with respect to the insulating film, polishing can be stopped when the surface of the insulating film 302 is exposed. In damascene, when the interconnection layers are formed, the surfaces of the interconnection layers and the upper surface of the insulating film have been planarized and flush with each other. Therefore, the surface of the insulating film need not be planarized. In formation of a multilayered interconnection structure in accordance with damascene, xe2x80x9cformation of an insulating filmxe2x80x94formation of trenchesxe2x80x94formation of interconnection layersxe2x80x9d is repeated a predetermined number of times.
Another conventionally known method will be described. As shown in FIG. 4A, an interlayer film 402 is formed on a substrate 401, and trenches 403a and 403b with predetermined shapes are formed at predetermined portions of the interlayer film 402.
As shown in FIG. 4B, a polyimide resin film 404 is formed on the interlayer film 402 including the interiors of the trenches 403a and 403b, so the trenches 403a and 403b are filled with polyimide resin.
Finally, as shown in FIG. 4C, the polyimide resin film 404 is polished by CMP until the surface of the interlayer film 402 is exposed, while leaving the polyimide resin only in the trenches 403a and 403b, thereby forming patterns 404a and 404b. In CMP, if the polyimide resin is selectively polished with respect to the material of the interlayer film 402, polishing can be stopped when the surface of the interlayer film 402 is exposed.
CMP used in damascene described above is a very effective means if a sufficiently high polishing selectivity can be maintained between a film to be polished and a film not to be polished. Even if a sufficiently high polishing selectivity cannot be maintained, when the film not to be polished is as thin as about 1 xcexcm, CMP is still effective as a planarizing means.
When a polishing target for CMP is a thick film with a thickness of about 10 xcexcm as in formation of a micromachine, it is very difficult to determine the end of polishing, and the polishing rate must be inevitably reduced, leading to an increase in polishing time.
When the film thickness increases to as large as 10 xcexcm, variations in thickness increase. When this film is polished by CMP, even if polishing is ended at a certain region, a film to be polished still remains at another region, making it very difficult to determine the end point. For this reason, conventionally, coarse polishing is performed first, and then finish polishing is performed by decreasing the polishing rate very low so the polishing selectivity is increased. In this manner, when a film with a thickness of about 10 xcexcm is to be planarized by polishing in accordance with CMP, it conventionally takes a very long time, for example, to form a micromachine by using damascene.
It is a principal object of the present invention to provide a pattern forming method which can planarize a comparatively thick film with a thickness of about 10 xcexcm within a shorter period of time than in the prior art.
In order to achieve the above object, according to the basic idea of the present invention, a portion to be polished by CMP is made present only near a desired pattern.
According to the present invention, there is provided a pattern forming method comprising the steps of forming a recess in a flat base, arranging a pattern material only in and around the recess so as to project upward from a surface of the base and to be larger than an opening of the recess, and removing the pattern material projecting from the surface of the base by chemical mechanical polishing (CMP) so as to be flush with an upper surface of the base.